Plotting curves with different scales in the same graph

I want to plot in the same graph two curves corresponding to two drugs' dose-response curves. The problem is that the concentrations are very different (nM values for drug A and microM for drug B...). How can I put these 2 curves in only 1 graph, but with a logarithmic scale in the x axis?

In excell it is not possible in a normal graph but with some creativity you can get a result.
Make both grafics and chose for the background in the drawing area and grafics area no fill.
Chose for the grafic area for both grafics the same sheet and you will see both grafics then it's just adjusting the scales and numbers.
I hope it's explained enough to get you going.